The overall objectives of this project are: 1. To provide diagnostic service to physicians who suspect glycogen storage disease or related disease in their patients. Enzyme assays are done in serum, urine and blood cells and only in a few cases with biopsy material. 2. New methods for diagnosis and further differentiation (detection of micro heterogeneity within one defect) of the glycogen-storage diseases are to be developed using easily available materials such as serum, urine and blood cells and if possible avoiding the use of biopsy material. Immediate goals are the assay of phosphorylase phosphatase in blood cells as well as further characterization of phosphorylase and phosphorylase kinase.